The present invention relates to a vapor-liquid ejector with a nozzle that is removable (or dismountable).
This type of device is known per se. It enables a liquid to be entrained by means of a driving fluid: namely the vapor. Said vapor passes through the nozzle of the device which transforms its pressure into speed. The nozzle is usually of the xe2x80x9csupersonicxe2x80x9d type having a converging-diverging profile which serves to increase outlet speed compared with that which would be obtained using a converging-only nozzle. Optimum efficiency is obtained by bringing the pressure of the vapor close to the suction pressure of the liquid. On coming into contact with the driven liquid, the vapor condenses very quickly, but not instantly. There generally remains a xe2x80x9cdartxe2x80x9d of vapor in the form of a converging cone at the outlet from the nozzle.
The driving fluid is generally steam, but there is no a priori reason why some other kind of vapor should not be used, providing its physical conditions are suitable and it does not pollute the driven liquid.
Whatever the kind of vapor used, the ejector nozzle which is engaged removably in the body of said ejector is raised to a relatively high temperature because of the flow of said vapor through the nozzle, thus making it a part which is sensitive to attack by corrosion. This problem is particularly applicable to the portion of the nozzle which is in contact with the driven liquid.
In any event, the problem of corrosion is critical in the clearance that must be present in order to enable the removable nozzle to be engaged in the body of the ejector, which clearance is accessible to the driven liquid and, with reference to said liquid, constitutes a kind of dead zone.
Crevice corrosion inevitably develops in said clearance.
The present invention has been developed with reference to this problem of corrosion in the structure of vapor-liquid ejectors having removable nozzles.
To make the invention easier to describe and also easier to understand, the present description begins with reference to the accompanying FIG. 1 by describing the structure of prior art removable-nozzle vapor-liquid ejectors. On sight of said structure, the above-mentioned corrosion problem can easily be understood. With respect to said problem, the present invention proposes an improvement to the structure of such prior art removable-nozzle vapor-liquid ejectors.
As shown in section in FIG. 1, the body 10 of such a prior art ejector 1 (and more precisely a recess 14 in said body 10) contains a nozzle 2 which is removably engaged therein. Said body 10 is provided:
with a first duct 11 for feeding said nozzle 2 with vapor V, i.e. the driving fluid; and
with a second duct 12 downstream from the first duct 11 along the axis of said nozzle 2 and relative to the flow direction of said vapor V, for the purpose of introducing the driven liquid L into said body 10.
Said nozzle 2 is positioned in stable manner in the recess 14 of said body 10, coming into abutment against an internal shoulder 13 of said body 10. A shoulder 3 of said nozzle 2 co-operates with said shoulder 13.
Sealing means 9 are located at the facing surfaces of said shoulders 3 and 13, i.e. the surfaces 3xe2x80x2 and 13xe2x80x2, which sealing means are for preventing the liquid L that is driven through the duct 12 from rising further upstream.
The sealing means 9 define two zones 14xe2x80x2 and 14xe2x80x3 in the recess 14 of said body 10 of the ejector 1:
an upstream zone 14xe2x80x2 which, in theory, is not accessible to the liquid L; and
a downstream zone 14xe2x80x3 which is accessible to the liquid L, which zone begins with an interstitial volume v which is generally annular insofar as said recess 14 and said nozzle 2 (over a fraction of its length) are generally cylindrical in shape. This volume corresponds to clearance enabling the nozzle 2 to be assembled in the recess 14 in the body 10 of the ejector 1. This clearance is provided between the outside surface 4 of the body of the nozzle 2 where it extends downstream from the shoulder 3 of said body of said nozzle 2, and the surface 13xe2x80x3 of the inner shoulder 13 of the body 10 of the ejector 1 which faces said outer surface 4 of the body of said nozzle 2. The volume extends along the axis of said nozzle 2 over a length that goes from said shoulder 3 of said body of the nozzle 2 (the sealing means 9) to level with the location where said driven liquid L is introduced via the second duct 12 into the downstream zone 14xe2x80x3 of the recess 14 in the body 10 of the ejector 1 (the arrival zone of said liquid L).
On observing FIG. 1 and on reading the above, the person skilled in the art will already have understood that the above-mentioned corrosion is critical in said interstitial volume v where the driven liquid L is heated by coming into contact with the outer surface 4 of the nozzle 2 and where it tends to stagnate. In prior art ejector structures, this volume v generally has a thickness e that is constant and equal to about 0.2 millimeters (mm).
In the invention, it is proposed to modify the internal structure of such ejectors in order to minimize corrosion problems in said volume v.
It has been found that two types of modification are necessary to obtain the desired effect (to transform said volume v from a dead zone to a genuinely dynamic zone):
said volume v must be enlarged; and
means must act to ensure that said enlarged volume v is swept by (non-stagnant) liquid;
surprisingly, it has been found that these modifications do not significantly degrade the hydraulic performance of the ejector in question.
The main object of the present invention is thus to provide a novel removable-nozzle vapor-liquid ejector of the type shown in accompanying FIG. 1 and modified in the manner outlined above.
Said novel ejectors thus comprise in conventional manner a body having a recess that receives a removable nozzle, said body of said ejector presenting:
a first duct for feeding said nozzle with vapor;
a second duct downstream from said first duct along the axis of said nozzle relative to the flow direction of said vapor and serving to introduce the driven liquid into said recess of said body; and
between said first and second ducts, an internal shoulder against which a shoulder of the body of said nozzle comes into abutment, sealing means being interposed between the facing surfaces of said two shoulders to prevent the driven liquid rising upstream from said sealing means; a (generally annular) interstitial volume inherent to said engagement then existing between the outer surface of the body of said nozzle where it extends downstream from the shoulder of said body of said nozzle and the surface of the internal shoulder of the body of the ejector facing said outer surface of the body of said nozzle, said (generally annular) interstitial volume extending along the axis of said nozzle over a length that goes from the shoulder of said body of said nozzle to the level where the driven liquid is introduced into said body of said ejector via the second duct and giving said driven liquid access to said sealing means.
In novel manner, said ejectors of the present invention present within the above-specified conventional structure, the following two characteristics:
said (generally annular) interstitial volume has a thickness of at least 2 mm over its entire length developed along the axis of the nozzle; and
on its outside surface, said nozzle has means facing said second duct that are suitable for directing at least a fraction of the driven liquid flow towards the sealing means via said (generally annular) interstitial volume.
These two characteristics in combination make it possible to achieve the desired result, i.e. to minimize corrosion in said (generally annular) interstitial volume by ensuring that the liquid genuinely flows within said volume with this flow of said liquid generally giving rise to significant cooling of said zone.
The thickness exe2x89xa72 mm of said volume can be constant or otherwise along its length. Advantageously, it is not constant. It can vary continuously or discontinuously. Advantageously, it varies continuously (without any edge at a step). Whichever variant is used, it is advantageously larger downstream than upstream (i.e. larger at the downstream end of said volume via which the driven liquid enters and leaves said volume than at the level of the sealing means).
Said volume may or not be symmetrical.
In a particularly advantageous variant, the (generally annular) interstitial volume is of thickness that is not constant, said thickness increasing progressively from downstream to upstream over at least a fraction of its length, and preferably over its entire length. In this advantageous variant, there is thus a thickness of at least 2 mm at the level of the sealing means at the upstream end of said interstitial volume, and a thickness of more than 2 mm over at least a fraction of the length of said volume, which thickness is at a maximum at the downstream end of said interstitial volume, with the driven liquid penetrating into said volume (and leaving said volume) via said downstream end.
The person skilled in the art will have understood that the xe2x80x9cenlargedxe2x80x9d interstitial volume can be implemented in various shapes.
Clearly the shape of the interstitial volume depends on the shapes of the facing surfaces that define it: the outer surface of the nozzle immediately downstream from the sealing means and the facing inner surface of the recess in the body of the ejector.
To ensure that said volume is of thickness that is not constant and that increases going from upstream towards downstream over at least a fraction of its length, it is strongly recommended to use one and/or the other of the following two techniques.
Firstly, the outer surface of the body of the nozzle, extending downstream from the shoulder of said body (in the portion which is accessible to the liquid in the recess in the body of the ejector), corresponds to the shape of a truncated cone over at least the downstream fraction of the length of the interstitial volume, and advantageously over its entire length. The base of said cone is naturally located upstream. The angle of inclination (from upstream to downstream) of said outer surface of the body of said nozzle relative to the axis of said nozzle generally lies in the range 3xc2x0 to 7xc2x0, and is advantageously at least 5xc2x0. It will be understood that the greater said angle, the greater the extent to which the corresponding interstitial volume is open.
Secondly, in order to open said volume, it is recommended to take action in the opposite direction on the inclination (relative to the axis of said nozzle) on the surface facing the outer surface of the body of the nozzle: the surface of the inner shoulder of the body of the ejector. With this second technique, said surface of the inner shoulder of the body of the ejector facing said outer surface of the body of the nozzle (immediately downstream from the sealing means, in the interstitial volume) flares from upstream to downstream relative to the axis of the nozzle over at least the downstream fraction of the length of the interstitial volume and advantageously over its entire length. The flare angle is advantageously less than or equal to 5xc2x0 (its angle of inclination relative to the axis of the nozzle).
It will naturally be understood that in order to obtain maximum opening of the interstitial volume, it is advantageous to combine the two above techniques by inclining both facing surfaces in opposite directions.
In a particularly preferred variant, the interstitial volume is enlarged as follows:
said outer surface of the body of said nozzle extending downstream from the shoulder of said body corresponds over its entire length to the surface of a truncated cone that slopes relative to the axis of said nozzle from upstream to downstream at an angle that is advantageously at least 5xc2x0; while
the surface of said internal shoulder of the body of the ejector facing said outer surface of the body of said nozzle extends from upstream to downstream over a downstream major fraction (advantageously over more than two-thirds) of the length of said interstitial volume flaring relative to the axis of said nozzle at an angle that is advantageously less than or equal to 5xc2x0 (measured relative to said axis).
Insofar as the parts concerned are generally cylindrical, with a cylindrical ejector having a cylindrical recess formed in its body to receive a nozzle that is cylindrical at least in its portion upstream from the sealing means therein with clearance, it will be understood that the interstitial volume corresponding to said clearance is generally of the annular type and, given the comments made above relating to its thickness which advantageously increases continuously from upstream to downstream, it is advantageously tubular in shape being defined by two coaxial frustoconical surfaces.
Concerning the means arranged in characteristic manner on the outer surface of the nozzle in order to direct the driven liquid into the xe2x80x9cenlargedxe2x80x9d interstitial volume, these can exist in various forms. These means can be referred to as xe2x80x9cdeflectorsxe2x80x9d.
They can be provided in particular in one or other of the following variants, namely:
they can be machined directly in the material forming said nozzle; and/or
they can be separate pieces fitted to the outer surface of said nozzle.
In the first case, they can be recessed portions such as channels or grooves formed in the body of said nozzle or else they can be portions in relief forming projections.
In the second case, an additional piece is secured to the outside surface of said nozzle which is equivalent to making portions in relief in the first case.
Said means arranged on the outer surface of the nozzle in order to direct the driven liquid into the enlarged interstitial volume, whether they be additional pieces fitted on said nozzle or shapes machined in its material, can comprise in position at least one washer portion (secured to said outer surface of said nozzle) having its bottom portion situated on the axis of the second duct (through which the driven liquid arrives) and having its top portion close to the inlet to the interstitial volume. xe2x80x9cTopxe2x80x9d and xe2x80x9cbottomxe2x80x9d are used herein on the understanding that the liquid is generally moving upwards on entering the ejector. In any event, the washer or washer portion acts to deflect the liquid into the interstitial volume.
In such a variant, said means advantageously consist in:
an elliptical washer (sloping relative to the axis of the nozzle so as to present top and bottom portions as mentioned above); or
an open washer (sloping relative to the axis of the nozzle so as likewise to present top and bottom portions as specified above; amounting to part of an elliptical washer), with the bottom edge of the opening being extended along the axis of the nozzle at the level of said axis by a rib extending itself towards the sealing means at the upstream end of the enlarged interstitial volume (although without touching said end). Said washer advantageously projects at 90xc2x0 to the outer surface of the nozzle.
This latter embodiment of the means arranged on the outer surface of the nozzle to deflect the driven liquid into the enlarged interstitial volume (whether the means are fitted or machined in the mass of the nozzle) is particularly preferred. It makes it possible to have full control over the flow of liquid into said interstitial volume and within it, and it ensures a significant decrease in the temperature within said volume.
It operates as follows. A fraction of the flow of liquid entering via the second duct is channeled by the action of the rib. Turning motion is imparted to the liquid towards and into the (generally annular) interstitial volume between the nozzle and the body of the ejector. At the end of this turning movement (sweeping said interstitial volume), the liquid in question leaves via the opening in the washer and rejoins the flow of liquid that is driven directly.
The person skilled in the art will readily understand that other variants of the means concerned will enable the same result or an equivalent result to be obtained in equally advantageous manner.
Specifically, the person skilled in the art will understand that ejectors of the invention can exist in a wide variety of variants: the xe2x80x9cenlargedxe2x80x9d interstitial volume can have a variety of shapes and likewise the xe2x80x9cdeflectorsxe2x80x9d on the engaged nozzle can have a variety of shapes.
Naturally, when the deflectors operate in relief it is necessary to ensure that they do not prevent the nozzle being installed (on engagement) and that they do not prevent the nozzle being removed from the body of the ejector. They must be dimensioned appropriately.
In another aspect, the present invention provides a nozzle for constituting the removable nozzle of a vapor-liquid ejector of the invention, as described above. In characteristic manner, the outer surface of the nozzle has means, recessed or in relief, suitable for directing upstream at least a fraction of the liquid flow that is driven by the ejector in which said nozzle is to be mounted.
Said means, as described above and advantageously constituting an open washer with a rib can either be machined in the mass of said nozzle or else they can be constituted by one or more pieces added thereto.
In a preferred embodiment, the nozzle in question has a converging-diverging profile and said means are positioned on the outer surface of the converging portion of said nozzle.
It is observed at this point that in general the profile of the nozzle in an ejector structure of the invention is advantageously converging-diverging.
The use of ejectors of the invention is particularly recommended when transferring xe2x80x9ccorrosivexe2x80x9d liquids, e.g. suspensions of acids charged with particles. Such ejectors of the invention turn out to withstand corrosion much better than prior art ejectors. The Applicant particularly recommends use of such ejectors for transferring radioactive liquids, with the ejector being mounted through the wall of an active cell.